1. Field of the Invention
The invention relates to reflective surfaces for use in virtual reality display devices, and more particularly to a method for making large highly reflective metal reflector plates for applications in game chips or similar virtual image projection systems.
2. Description of the Related Art
Large reflective surfaces on integrated circuits are needed for applications such as virtual reality display devices. IEEE Spectrum, October 1993, pages 22-40 "Special Report: Virtual Reality is for Real" covering several papers, gives a general discussion of current virtual reality technology, wherein a very natural interface between humans and computers is created. Communication between a human and computer can take the form of moving 3-dimensional imagery, spatial sounds and even physical forces from motion to touching.
There is currently a need to provide large reflective metal, or the like, surfaces on the surface of integrated circuit memory chips for use in virtual reality display devices. I/O (Input/Output) pads with large metal surfaces are currently used on integrated circuit chips, but are not nearly large enough for a reflective metal area for virtual reality display purposes. Nor are I/O pads reflective enough to be used as reflective surfaces. Current capability for specularity, the degree of light that is scattered, is only 2%, while a specularity of about 80% is desirable.
In the prior art structure shown in FIG. 1, a memory cell has been formed on semiconductor substrate 10, including field oxide isolation regions 12, polysilicon layers 14 and 16, all formed as is well known in the art. An insulating layer 18 is formed on second polysilicon layer 16 and in openings in the polysilicon. This layer is formed of typically silicon oxide or the like. A first metal layer 20 is deposited and patterned, is typically of aluminum and is used for interconnection of devices to each other and to input/output pads. An intermetal dielectric (IMD) layer 22 is deposited over and between metal layer 20. It will be noted that each successive layer's top surface is uneven, due to the uneven surface on which the layers are deposited. A second metal layer is now deposited on the IMD layer and is typically aluminum. This metal layer is then patterned to form a metal pad 24, for I/O purposes and the like, and a passivation layer 26 is deposited and patterned above it to expose the metal pad. As shown in FIG. 1, the top surface is rough and uneven, due to the uneven nature of the top surface of the IMD layer beneath it, and due to the metal layer itself. The metal top surface is unacceptable for a reflector plate, but is adequate for I/O pads and the like, as the uneven surface will cause destructive interference of light waves impacting on the plate.